What is heat?

Maybe you are playing outside on a hot day and you walk into your house that is nice and cool. Ahhh…

But, what exactly is heat? Well, heat is really just the motion of the atoms around you.
What! That’s crazy!

Just like little bouncy balls bouncing around in a room, atoms and molecules are always bouncing off of each other… all the time… all around us.

If you think of a room full of little bouncy balls, they would just be lying not moving at all if there was nothing to start them bouncing. Gravity would pull them to the ground and they would sit there. It takes some form of energy to get these bouncy balls bouncing. You could start throwing some of the balls around. One ball would hit another and eventually more balls would be bouncing around. The motion of those balls (the atoms and molecules all around us) is what we call heat.

If you are in a house with one room that has the air conditioner running and is a chilly 20 degrees and another room that doesn’t have an air conditioner and is 100 degrees. What happens if you open the door between those rooms and wait a few minutes? The temperature slowly becomes the same between the two rooms. It’s sort of like playing a game of atomic pool. When you open the door, the fast moving warm (100 degree) air molecules start banging into the slower moving cooler (20 degree) molecules. When they bang into each other, they start to transfer motion. Throughout the 2 rooms; fast molecules hit slow ones… the slow ones speed up and the fast ones slow down. Try opening the door below by clicking on the red bar (it will turn green). Note: you may not be able to see the image below on an iPad or iPhone.

What are some things that produce heat?
Well, the sun is a big heat producer. It produces enough energy to heat the entire earth!
But how..?
The sun releases a LOT of energy in the form of light and other Electromagnetic waves. These waves travel at 186,000 miles a second (or 300,000 kilometers per second using the metric system). When those waves come in contact with atoms and molecules, they add a lot of energy and start the molecules and atoms moving faster. The difference between an ice cube, water, and water that has evaporated is just how fast the water molecules are moving.

Nerves in out body sense this increasing motion or decreasing motion and send signals to our brain. Our brain interprets those signals as hot or cold.

Cold air will also sink at first and the hot air will rise. Why? Because there are more molecules closer to each other in the cold air so gravity pulls harder on it. The warm air rises mostly because the cold air pushes it up.

If you went outside on a hot day and blew up a balloon, then brought it inside and put it in a bucket of ice water… you should see the balloon shrink a little. Why does this happen? Well, the warm air has molecules that are bouncing around really fast and those molecules are bouncing into the inside of the balloon pretty hard keeping it inflated. If you slow those molecules down by putting the balloon in ice water, the molecules are bouncing around more slowly and they are not hitting the inside of the balloon as hard so it looks a little less inflated. The balloon hasn’t lost any molecules… they are just closer together inside the balloon because the molecules are not bouncing off each other as much.